1. Field of Invention
The present invention relates to a manual cut-off system for passive safety devices and, more particularly, relates to such a system suited to accurately maintain operability of each of a plurality of air bags even after those air bags have been required to operate. The present invention also relates to a manual cut-off method for passive safety devices.
2. Description of Related Art
For example, U.S. Pat. No. 5,544,914 discloses a system wherein a vehicle passenger can manually change operability of an air bag.
The system according to this related art is equipped with a fuse connected in parallel with a squib corresponding to the air bag and a switch for selectively connecting a source of ignition signals to the squib or the fuse. When the air bag is required to operate, the source of ignition signals generates an ignition signal that is sufficient to ignite the squib and cut the fuse. The switch connects the source of ignition signals to the squib before the vehicle passenger requires that the air bag be capable of operation. On the other hand, if the vehicle passenger requires that the air bag be prevented from operating, the switch connects the source of ignition signals to the fuse.
If the air bag is required to be deployed under the circumstance where the vehicle passenger demands operation of the air bag, the ignition signal generated by the aforementioned source is supplied to the squib, thus deploying the air bag. On the other hand, if the air bag is required to be deployed under the circumstance where the vehicle passenger demands prevention of operation of the air bag, the ignition signal generated by the source is supplied to the fuse, thus cutting the fuse without deploying the air bag.
Hence, it is possible to determine whether or not the vehicle passenger had demanded prevention of operation of the air bag before a requirement for deployment thereof, by checking whether or not the fuse has been cut after the requirement for deployment of the air bag.
However, a surge current or a noise current may flow through the fuse. Thus, there is a possibility of the fuse being cut before arrival of the ignition signal. On the contrary, even if the ignition signal has been supplied to the fuse, the fuse may not be cut owing to, for example, characteristic errors or the like. Therefore, according to a system wherein the state manually set by the vehicle passenger is determined based on the state of the fuse, there is a possibility of an inaccurate judgement being made.
In addition, the system according to the related art is incapable of determining whether or not the switch for connecting the source of ignition signals to one of the squib and the fuse is in normal operation. Hence, even if there is a failure in the switch, the vehicle passenger is not informed of such a failure immediately.
Furthermore, in the case where a plurality of air bags are mounted to the vehicle, the system according to the related art requires that a plurality of switches and fuses be provided in correspondence with the respective air bags (as well as the respective squibs). For this reason, if the system according to the related art is employed in the case where a plurality of air bags are provided, the overall dimension of the system may increase substantially.